Systems for processing differentiated hierarchical modultation used in radio frequency communications

ABSTRACT

The present invention employs hierarchical modulation to simultaneously transmit data over different modulation layers using a carrier RF signal. Each modulation layer may be of a higher or lower order than the other modulation layers. Certain embodiments of the present invention may transmit different information on the different modulation layers. Other embodiments of the present invention may use the different layers for processing information differently.

This application is a continuation application of co-pending U.S. patentapplication Ser. No. 11/945,162, entitled PROCESSING DIFFERENTIATEDHIERARCHICAL MODULATION USED IN RADIO FREQUENCY COMMUNICATIONS, filedNov. 26, 2007, which is a Continuation-in-Part of U.S. patentapplication Ser. No. 11/618,774, entitled CONTENT DIFFERENTIATEDHIERARCHICAL MODULATION USED IN RADIO FREQUENCY COMMUNICATIONS, filedDec. 30, 2006, which issued as U.S. Pat. No. 7,986,746, both of whichare incorporated herein by reference in their entireties.

This application claims the benefit of provisional patent applicationSer. No. 60/882,921 entitled MODULATION DIVISION MULTIPLE ACCESS, filedDec. 30, 2006, the disclosure of which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to radio frequency (RF) transmittermodulation techniques used in RF communications systems.

BACKGROUND OF THE INVENTION

With each successive generation of RF communications systems, modulationtechniques, access schemes, and communications protocols become moresophisticated and demanding. One universal goal is to increase theamount of information transmitted in a given communications band, and toaccommodate different types of information that must be communicated.For example, first generation cellular networks were designed to provideonly voice services; however, these networks have evolved to provide anumber of simultaneous services, including internet traffic, such asemails, and provide multi-media services, such as broadcast andon-demand services in specific geographic areas. Each of these servicesmay have its own specific requirements for bandwidth, latency,acceptable error rate, and locations of availability. As a result,different processing methods have been developed, including orthogonalfrequency division multiplexing (OFDM), single carrier frequencydivision multiplexing (SC-FDM), single frequency networks (SFN),multiple-input multiple-output (MIMO), and multi-hop and relayedtransmissions. OFDM and SC-FDM can distribute a high bandwidth signalonto multiple sub-carriers of lower bandwidths. SFNs improve signalcoverage of broadcast data by transmitting the same information at thesame time from multiple antennas. MIMO adds antennas to a system toprovide spatial multiplexing, diversity, or both. Multi-hop and relayedtransmissions provide improved system capacity or extended coverage byrelaying transmissions through multiple transceiver stations. Therefore,as communications systems evolve, there is a need to increase the numberand diversity of services by improving how bandwidth is utilized.

SUMMARY OF THE INVENTION

The present invention employs hierarchical modulation to simultaneouslytransmit data over different modulation layers using a carrier RFsignal. Each modulation layer may be of a higher or lower order than theother modulation layers. Certain embodiments of the present inventionmay transmit different information on the different modulation layers.Other embodiments of the present invention may use the different layersfor processing information differently.

Transmitting different information on different modulation layers mayprovide many useful applications. Unicast data is transmitted to asingle user, whereas broadcast data is transmitted to multiple users.The present invention includes any combination of unicast data andbroadcast data to be transmitted using any combination of the differentmodulation layers. Unicast data and broadcast data include differenttypes of content, including audio content, video content, voice content,and specific data content.

Audio content may provide at least one channel of audio programming,which may provide an on-demand audio program that is unicast to a singleuser, or distributed audio programs that are broadcast to multipleusers. Similarly, video content may provide at least one channel ofvideo programming. Voice content may include individual cellulartelephone calls. Specific data content may include internet data,including emails, short messaging service messages, or downloadedinformation. The present invention includes any combination of types ofcontent to be transmitted using any combination of the differentmodulation layers.

In the present invention, the different information on differentmodulation layers may be transmitted to different geographic areas. Thecontent of the different information may be associated with differentgeographic areas. One example is a national news program that may bebroadcast to a large geographic area from multiple base stations usingone modulation layer, and a local traffic program that may be broadcastto a subset of the large geographic area from one base station using adifferent modulation layer.

The present invention may include using the different modulation layersin conjunction with other techniques for processing differentinformation streams. One modulation layer may be used to providebroadcast data to multiple base stations that form a single frequencynetwork (SFN). An SFN may be used to improve signal coverage ofbroadcast data by transmitting the same information at the same timefrom multiple antennas.

MIMO adds antennas to a system to provide spatial multiplexing,diversity, or both. The information transmitted from MIMO antennas maybe provided from any combination of the different modulation layers. Theadditional MIMO antennas may be used to strengthen an SFN. Onemodulation layer may be used to provide broadcast data, which istransmitted from multiple MIMO antennas simultaneously. Anothermodulation layer may be used to provide multiple channels of data, whichare transmitted from different MIMO antennas.

Video broadcast data may have high bandwidth requirements. OFDM orSC-FDM can distribute a high bandwidth signal onto multiple sub-carriersof lower bandwidth. The present invention may be used to providedifferent sub-carriers using different modulation layers, or to provideat least one sub-carrier using one modulation layer, and otherinformation using at least one other modulation layer.

Multi-hop and relayed transmissions provide broadcast data or othersystem data to multiple base stations. The present invention may be usedto provide any combination of system data, relayed data, and end userdata using any combination of modulation layers. Certain modulationtechniques may include one or more modulation layers that are compatiblewith modulation techniques that are used in existing communicationsnetworks. Therefore, the present invention may provide compatibilitybetween different communications systems by using compatible modulationlayers, which may allow an upgraded communications system to be backwardcompatible with legacy user equipment (UE).

Those skilled in the art will appreciate the scope of the presentinvention and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 shows an RF communications system.

FIG. 2A shows a modulation symbol having four bits of information.

FIG. 26 shows one embodiment of the present invention wherein themodulation symbol illustrated in FIG. 2A is divided into a lowermodulation symbol and a higher modulation symbol.

FIG. 3 shows the present invention used with quadrature modulation.

FIG. 4 shows the four constellation points used in quadrature phaseshift keying (QPSK) modulation, and their relationship with the lowermodulation symbol.

FIG. 5 shows the sixteen constellation points used in rectangularsixteen quadrature amplitude modulation (16-QAM), and their relationshipwith the lower modulation symbol.

FIG. 6 shows the four constellation points used in the first quadrant of16-QAM.

FIG. 7A shows the alignment of lower modulation layer data with highermodulation layer data in one embodiment of the present invention.

FIG. 7B shows the lower modulation layer data time-shifted from thehigher modulation layer data in an alternate embodiment of the presentinvention.

FIG. 8A shows time multiplexed data included in the higher modulationlayer data.

FIG. 8B shows two single-frequency OFDM sub-carriers included in thehigher modulation layer data.

FIG. 9 adds MIMO antennas to the base stations and some of the terminalsillustrated in FIG. 1.

FIG. 10 shows single-input single-output (SISO) data included in thelower modulation layer data, and two MIMO sub-channels included in thehigher modulation layer data.

FIG. 11 shows the present invention used with MIMO transmittercircuitry.

FIG. 12 shows details of the first base station illustrated in FIG. 1.

FIG. 13 is a block representation of a cellular communication system.

FIG. 14 is a block representation of a base station according to oneembodiment of the present invention.

FIG. 15 is a block representation of a mobile terminal according to oneembodiment of the present invention.

FIG. 16 is a logical breakdown of an OFDM transmitter architectureaccording to one embodiment of the present invention.

FIG. 17 is a logical breakdown of an OFDM receiver architectureaccording to one embodiment of the present invention.

FIG. 18 illustrates a pattern of sub-carriers for carrying pilot symbolsin an OFDM environment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the invention and illustratethe best mode of practicing the invention. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the invention and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

The present invention employs hierarchical modulation to simultaneouslytransmit data over different modulation layers using a carrier RFsignal. Each modulation layer may be of a higher or lower order than theother modulation layers. Certain embodiments of the present inventionmay transmit different information on the different modulation layers.Other embodiments of the present invention may use the different layersfor processing different information streams.

Transmitting different information on different modulation layers mayprovide many useful applications. Unicast data is transmitted to asingle user, whereas broadcast data is transmitted to multiple users.The present invention includes any combination of unicast data andbroadcast data to be transmitted using any combination of the differentmodulation layers. Unicast data and broadcast data include differenttypes of content, including audio content, video content, voice content,and specific data content.

Audio content may provide at least one channel of audio programming,which may provide an on-demand audio program that is unicast to a singleuser, or distributed audio programs that are broadcast to multipleusers. Similarly, video content may provide at least one channel ofvideo programming. Voice content may include individual cellulartelephone calls. Specific data content may include internet data,including emails, short messaging service messages, or downloadedinformation. The present invention includes any combination of types ofcontent to be transmitted using any combination of the differentmodulation layers.

In the present invention, the different information on differentmodulation layers may be transmitted to different geographic areas. Thecontent of the different information may be associated with differentgeographic areas. One example is a national news program that may bebroadcast to a large geographic area from multiple base stations usingone modulation layer, and a local traffic program that may be broadcastto a subset of the large geographic area from one base station using adifferent modulation layer.

The present invention may include using the different modulation layersin conjunction with other techniques for processing differentinformation streams. One modulation layer may be used to providebroadcast data to multiple base stations that form a single frequencynetwork (SFN). A SFN may be used to improve signal coverage of broadcastdata by transmitting the same information at the same time from multipleantennas.

Multiple-input multiple-output (MIMO) adds antennas to a system toprovide spatial multiplexing, diversity, or both. The informationtransmitted from MIMO antennas may be provided from any combination ofthe different modulation layers. The additional MIMO antennas may beused to strengthen an SFN. One modulation layer may be used to providebroadcast data, which is transmitted from multiple MIMO antennassimultaneously. Another modulation layer may be used to provide multiplechannels of data, which are transmitted from different MIMO antennas.

Video broadcast data may have high bandwidth requirements. Orthogonalfrequency division multiplexing (OFDM) or single carrier frequencydivision multiplexing (SC-FDM) can distribute a high bandwidth signalonto multiple sub-carriers of lower bandwidth. The present invention maybe used to provide different sub-carriers using different modulationlayers, or to provide at least one sub-carrier using one modulationlayer, and other information using at least one other modulation layer.

Multi-hop and relayed transmissions provide broadcast data or othersystem data to multiple base stations. The present invention may be usedto provide any combination of system data, relayed data, and end userdata using any combination of modulation layers. Certain modulationtechniques may include one or more modulation layers that are compatiblewith modulation techniques that are used in existing communicationsnetworks. Therefore, the present invention may provide compatibilitybetween different communications systems by using compatible modulationlayers, which may allow an upgraded communications system to be backwardcompatible with legacy user equipment (UE).

The present invention may be used to simultaneously download informationdirectly to UE and to transmit system information to systemtransceivers, such as repeaters, relays, or base stations. The systeminformation may include information for downloading by other systemtransceivers and synchronization information for broadcasting userinformation from multiple transceivers and antennas simultaneously. Thepresent invention may provide compatibility between differentcommunications systems having different modulation schemes, which mayallow an upgraded communications system to be backward compatible withlegacy UE. Additionally, low cost UE using the legacy modulation schemecould be feasible with such a system. For example, an upgraded systemusing multiple antennas, such as MIMO may be compatible with systemsusing single antennas, such as single-input single-output (SISO). Abasic broadcast channel may be transmitted using one modulation layerfrom all of the MIMO antennas, and multiple supplemental broadcastchannels may be transmitted using another modulation layer fromdifferent MIMO antennas. Legacy UE may receive the basic broadcastchannel; however, upgraded UE is required to receive the supplementalbroadcast channels.

Multiplexing is a processing technique for transmitting differentstreams of information using a common transmission entity. Frequencydivision multiplexing (FDM) transmits different streams of informationusing different frequencies. Time division multiplexing (TDM)interleaves different streams of information into a single combinedinformation stream, which is then transmitted. OFDM and SC-FDM maycombine with FDM and TDM to create multiple sub-carriers fortransmitting different streams of information. Other multiplexingtechniques may be used with OFDM and SC-FDM to provide additionalsub-carriers. MIMO is a multiple antenna architecture, which may providespatial multiplexing by allowing different information to be transmittedusing different antennas. The present invention is associated with a newmultiplexing technique called modulation division multiplexing (MDM),which transmits different information on different modulation layers.MDM may be associated with a new multiple access technique calledmodulation division multiple access (MDMA). The present invention may beused with a single, carrier RF signal, a multiple carrier RF signal, orboth. Any frequency or bandwidth RF signal may be used with the presentinvention.

Existing user equipment may be able to receive and transmit only thelower modulation layer, and ignore the higher modulation layer. Anupgraded system may be backward compatible with existing communicationsequipment using existing features, while adding additional features thatmay be supported with upgraded equipment. In one embodiment of thepresent invention, the hierarchical modulation method includesrectangular quadrature amplitude modulation (QAM), where lower layermodulation layer bits are encoded with only phase shifting, such as dataused with quadrature phase shift keying (QPSK), and upper modulationlayer bits are encoded with QAM; however, existing communicationsequipment may ignore the QAM data, bits and receive only those bitsencoded with QPSK.

Alternate embodiments of the present invention may use non-rectangularQAM. While rectangular QAM is easy to illustrate and describe,separation of encoded data bits may be such that the encoded data bitsare not equidistant from each other. Encoding of the data bits may bemodified to maximize signal margins, may compensate for effectsintroduced during transmission, reception, or both.

FIG. 1 shows an RF communications system 10, such as a cellularcommunications system, having a first base station 12 with a firstantenna port ANT1 coupled to a first base station antenna 14, a secondbase station 16 with the first antenna port ANT1 coupled to a secondbase station antenna 18, a first mobile terminal 20 with the firstantenna port ANT1 coupled to a first mobile antenna 22, a fixed terminal24 with the first antenna port ANT1 coupled to a fixed terminal antenna26, a second mobile terminal 28 with the first antenna port ANT1 coupledto a second mobile antenna 30, and a third mobile terminal 32 with thefirst antenna port ANT1 coupled to a third mobile antenna 34. Theantennas 14, 18, 22, 26, 30, 34 transmit and receive radiated RF signals36. The base stations 12, 16 control information flow to and from theterminals 20, 24, 28, 32, which are ideally controlled by whichever basestation is the closest, presents the best quality RF link, or both.

The radiated RF signals 36 are modulated to encode digital information.A number of modulation and encoding techniques may be used, includingfrequency modulation (FM) with frequency shift keying (FSK), phasemodulation (PM) with phase shift keying (PSK) or Gaussian Minimum ShiftKeying (GMSK), amplitude modulation (AM) with amplitude shift keying(ASK), or any combination thereof. One common modulation technique incellular communications systems is a combination of AM and PM, which isQAM, as described above. One common modulation technique in earlygenerations of cellular communications systems is QPSK, which can encodetwo bits of information with each modulation symbol, or phase shift.FIG. 2A shows a modulation symbol 38 having four bits of information,including bit zero 40, bit one 42, bit two 44, and bit three 46. Toencode four bits of information, sixteen different possible modulationpoints are required for each modulation symbol 38.

FIG. 2B shows one embodiment of the present invention by dividing themodulation symbol 38 illustrated in FIG. 2A into a lower modulationsymbol 48 and a higher modulation symbol 50. The lower modulation symbol48 includes bit two 44 and bit three 46. The higher modulation symbol 50includes bit zero 40 and bit one 42. The lower and higher modulationsymbols 48, 50 may encode information that is unrelated, that may be ondifferent channels or sub-channels, or that may be differentiated insome manner. Other embodiments of the present invention may divide themodulation symbol 38 into more than two hierarchical modulation symbols,such as the lower modulation symbol 48, the higher modulation symbol 50,and at least one supplemental modulation symbol.

The present invention may use a modulation symbol that may be dividedinto any number of sub-symbols. Each sub-symbol may include any numberof bits. The bits may be assigned to each sub-symbol in any order. Eachbit of data in a modulation sub-symbol may be used to transmit dataintended for one unique receiver only or for more than one receiver.Multiple bits of data in a modulation sub-symbol may be used to transmitdata intended for one unique receiver only or for more than onereceiver. Any receiver that receives transmitted data may receive all orpart of a modulation symbol. The receiver may process all or part of amodulation symbol. The receiver may receive one or more sub-symbols. Thereceiver may process one or more sub-symbols. The receiver may receiveone or more bits in a sub-symbol. The receiver may process one or morebits in a sub-symbol. For example, bit zero 40 may be used to transmitdata to a first receiver, bit one 42 may be used to transmit data to asecond receiver, bit two 44 may be used to transmit data to a thirdreceiver, and bit three 46 may be used to transmit data to a fourthreceiver. Alternatively, bit zero 40 may be used to transmit data to afirst receiver, bit one 42 may be used to transmit data to a secondreceiver, and bits two and three 44, 46 may be used to transmit data toa third receiver.

FIG. 3 shows one embodiment of the present invention used withquadrature modulation 52, which is associated with phase modulation.Phase-shifts may be represented graphically on a two-dimensional gridhaving an in-phase axis and a quadrature-phase axis. The two-dimensionalgrid may be divided into four quadrants, including a first quadrant 54,a second quadrant 56, a third quadrant 58, and a fourth quadrant 60. Ifthe four quadrants are used to represent four different possiblemodulation points, then two bits of information can be encoded, whichcould correspond to bits two and three 44, 46 of the lower modulationsymbol 48. The first quadrant 54 may be represented with bit two 44equal to zero and bit three 46 equal to zero. The second quadrant 56 maybe represented with bit two 44 equal to one and bit three 46 equal tozero. The third quadrant 58 may be represented with bit two 44 equal tozero and bit three 46 equal to one. The fourth quadrant 60 may berepresented with bit two 44 equal to a one and bit three 46 equal toone.

FIG. 4 shows the four constellation points used in QPSK modulation andtheir relationship with the lower modulation symbol 48, including bitstwo and three 44, 46. The four constellation points include a firstquadrant point 62, a second quadrant point 64, a third quadrant point66, and a fourth quadrant point 68. The four constellation points usedin QPSK have equal amplitudes and are differentiated only by phase;however, as long as the constellation points fall within the correctquadrant 54, 56, 58, 60, the lower modulation symbol 48, including bitstwo and three 44, 46 will be decoded correctly. This characteristic maybe beneficial in mixing a system with phase and amplitude modulation,such as QAM, with a system having only phase modulation, such as QPSK.The QPSK system may be able to reliably receive and transmit the lowermodulation symbol 48 in systems with QAM; therefore, upgradedcommunications equipment using QAM may be backward compatible withexisting communications equipment using QPSK for certain features. Inone embodiment of the present invention, a communications system mayalternate between transmitting QAM signals and QPSK signals. Otherembodiments of the present invention may use other combinations of FM,PM, and AM to provide hierarchical modulation systems. Some embodimentsof such systems may be backward compatible.

FIG. 5 shows the sixteen constellation points used in rectangularsixteen quadrature amplitude modulation (16-QAM), and their relationshipwith the lower modulation symbol 48. With sixteen different possiblemodulation points, then four bits of information can be encoded, whichcould correspond to bits two and three 44, 46 of the lower modulationsymbol 48 and bits zero and one 40, 42 of the higher modulation symbol50. The sixteen constellation points include a first quadrant firsthigher point 70, a first quadrant second higher point 72, a firstquadrant third higher point 74, a first quadrant fourth higher point 76,a second quadrant first higher point 78, a second quadrant second higherpoint 80, a second quadrant third higher point 82, a second quadrantfourth higher point 84, a third quadrant first higher point 86, a thirdquadrant second higher point 88, a third quadrant third higher point 90,a third quadrant fourth higher point 92, a fourth quadrant first higherpoint 94, a fourth quadrant second higher point 96, a fourth quadrantthird higher point 98, and a fourth quadrant fourth higher point 100.

FIG. 6 shows the four constellation points used in the first quadrant 54of 16-QAM, which includes the first quadrant points 70, 72, 74, 76. Ifthe four first quadrant points 70, 72, 74, 76 are used to represent fourdifferent possible modulation points, then two bits of information canbe encoded, which could correspond with bits zero and one 40, 42 of thehigher modulation symbol 50. The first quadrant first higher point 70may be represented with bit zero 40 equal to a zero and bit one 42 equalto a zero. The first quadrant second higher point 72 may be representedwith bit zero 40 equal to a one and bit one 42 equal to a zero. Thefirst quadrant third higher point 74 may be represented with bit zero 40equal to a zero and bit one 42 equal to a one. The first quadrant fourthhigher point 76 may be represented with bit zero 40 equal to a one andbit one 42 equal to a one. In one embodiment of the present invention,the phases and amplitudes separating the first quadrant points 70, 72,74, 76 from each other may be less than the phases and amplitudesseparating the groups of first quadrant points 70, 72, 74, 76, secondquadrant points 78, 80, 82, 84, third quadrant points 86, 88, 90, 92,and fourth quadrant points 94, 96, 98, 100 from each other. Therefore,the reliability of data provided with the lower modulation symbol 48,called lower modulation layer data, may be greater than that providedfor the higher modulation symbol 50, called higher modulation layerdata, particularly with wireless communications links with low signalmargins. In wireless communications links that operate with high signalmargins most of the time, the difference in the reliabilities may beindetectable; however, the reliabilities over time, called averagereliabilities, will show differences due to those situations that mayoccasionally produce low signal margins.

Broadcast data is data that is intended to be received by more than oneend user. Another frequently encountered term in communications ismulticast. One difference between broadcast data and multicast data isthat broadcast data may be intended for more end users-thanmulticast-data. Additionally, multicast data may be transmitted with anexpectation of an acknowledgement back from one or more end user. Inthis specification the term broadcast should be taken to mean broadcast,multicast, or both. Broadcast data may be audio, video, or both.Examples of broadcast data include video programs and audio programs.Broadcast data with national content may include network programs suchas national newscasts or movies. Broadcast data with regional contentmay include regional newscasts or statewide information programs.Broadcast data with local content may include weather or trafficinformation. Broadcast data with basic content may include networkchannels or news channels. Broadcast data with supplemental content mayinclude special interest channels, such as a sports channel or aneducational channel. Unicast data is data that is intended to bereceived by one end user. Examples of unicast data include voice unicastdata, such as cellular phone calls, specific unicast data, such as emailmessages, short message services, audio unicast data, such as anon-demand audio program, and video unicast data, such as an on-demandvideo program.

Broadcast data or unicast data may be transmitted using channels orsub-channels. A channel is a flow of information that contains all ofthe information associated with an information group, such as a videoprogram together with its associated audio channels and sub-titles.Sub-channels are used to divide a channel into multiple flows ofinformation for transmission over some medium, such as a cellularnetwork. The information group is reconstructed by combining thesub-channels. Sub-channels are commonly used when communicationschannels in a communications system have inadequate bandwidth to handlethe full bandwidth of the information being transmitted.

The present invention includes processing different information streamsusing different modulation layers. OFDM is a technique for distributingdata over a number of OFDM sub-carriers, which can be created by anumber of different methods, so long as each sub-carrier is orthogonalwith respect to other sub-carriers. In this context, orthogonal meanseach sub-carrier does not interfere with the other sub-carriers. Theorthogonality can be provided by using carriers at differentfrequencies, which is known as FDM and is associated with FDMA or OFDM,time multiplexing, which is known as TDM and is associated with TDMA,spatial multiplexing, which is associated with MIMO systems that havemultiple antennas such that each antenna may have different information,or any combination thereof. The present invention includes dividingmodulation symbols, called MDM associated with a new access techniquecalled MDMA. Related to OFDM is SC-FDM. The present invention may beused to provide one or more sub-carriers in an OFDM or SC-FDM system.Additionally, the present invention may be used with numerousmultiplexing techniques, including FDM, TDM, special multiplexing, MDM,OFDM, SC-FDM, or any combination thereof.

In one embodiment of the present invention, the modulation symbols 48,50 may include different types of information selected from thefollowing group, including video broadcast channels, video broadcastsub-channels, video unicast channels, video unicast sub-channels, audiobroadcast channels, audio broadcast sub-channels, audio unicastchannels, audio unicast sub-channels, voice unicast data, specificunicast data, OFDM data, OFDM sub-carriers, error correction bits, errorchecking bits, re-transmissions of information, received transmissionacknowledgements, and other system control information. Otherembodiments of the present invention may include more than two differentmodulation layers.

In one embodiment of the present invention, the lower modulation symbol48 includes broadcast data having national content, and the highermodulation symbol 50 includes broadcast data having local content. In analternate embodiment of the present invention, the lower modulationsymbol 48 includes broadcast data having basic content, and the highermodulation symbol 50 includes broadcast data having supplementalcontent. In an additional embodiment of the present invention, the lowermodulation symbol 48 includes information intended to be directlyreceived by UE. The higher modulation symbol 50 includes informationintended to be received by a relay station for forwarding to other relaystations, UE, or both. A base station may serve as a relay station. Asynchronization signal may be included to synchronize transmissions toUE from multiple base stations or relay stations. The informationincluded in the lower modulation symbol 48 may be repeated in the highermodulation symbol 50. The synchronization signal may include a preambleto facilitate synchronization.

The present invention includes processing different information streamsusing different modulation layers. Such processing may include providingan SFN. An SFN may be formed when multiple antennas in an RFcommunications system 10 transmit the same information on the samemodulation layer at the same time, which provides robust datatransmission since the multiple signals may fill in coverage holescaused by shadowing and multi-path effects; therefore, higher broadcastdata rates may be feasible with SFN. SFN data may be included in thelower modulation symbol 48, the higher modulation symbol 50, or both.Some or all of the broadcast data that incorporates the presentinvention may include SFN data.

The present invention employs hierarchical modulation to simultaneouslytransmit information on different modulation layers using a carrier RFsignal. In one embodiment of the present invention, first data to betransmitted is assigned to a first modulation layer and second data tobe transmitted is assigned to a second modulation layer based onreliability criteria. The first and second modulation layers arehierarchical modulation layers of the carrier RF signal. Once assigned,the first data is transmitted using the first modulation layer of thecarrier RF signal and the second data is transmitted using the secondmodulation layer of the carrier RF signal. One modulation layer isgenerally a higher order than the other modulation layer.

In one embodiment of the present invention, in many circumstances, thelower order modulation layer may be more reliable than the higher ordermodulation layer. In general, the reliability criteria takes thereliability characteristics of the different modulation layers intoaccount when assigning the first and second data to the differentmodulation layers. For example, reliability information may be derivedfrom signal strength measurements or channel conditions to determine anappropriate modulation to use for transmitting certain data.Alternatively, different data may be associated with differentpriorities in general, as well as different transmission priorities. Inanother example, entertainment channels may have a lower priority thanemergency service channels. Although maintaining data integrity isimportant for file transfers, the relative transmission priority for afile transfer is generally lower than that for voice or other streamingmedia. In essence, the reliability criteria may relate to thecommunication channels, the data being transmitted, the transmission ofthe data, any combination thereof, or the like. For the various data,the reliability information is used to assign the various data to thedifferent modulation layers for transmission.

In certain embodiments of the present invention, different data isbroadcast to multiple users using different modulation layers. Thedifferent data is assigned to specific modulation layers based onreliability criteria. In one embodiment of the present invention, asingle program is broken into two different data streams. One providesbasic resolution content while the other provides optional higherresolution content. Upon receipt of the lower resolution content, onlythe lower resolution version of the program is available. If the higherresolution content is available, the lower and higher resolutionversions of the program are combined to form a composite program of highresolution. With the present invention, the higher resolution content istransmitted using the higher order modulation layers and the lowerresolution content is transmitted using the lower order modulationlayers.

In voice applications, each modulation layer may support one or morevoice calls. As such, the reliability criteria is used when assigningdata for different voice calls to the different modulation layers. Somecalls are supported on higher order modulation layers while others aresupported on lower order modulation layers in light of the reliabilitycriteria.

In one embodiment of the present invention, the base stations 12, 16both transmit required broadcast data using the modulation layer withgreater reliability, and transmit optional broadcast data using themodulation layer with lesser reliability. In an alternate embodiment ofthe present invention, the base stations 12, 16 both transmit eithernational or regional data using the modulation layer with greaterreliability, wherein the first base station 12 transmits first localdata and the second base station 16 transmits second local data usingthe modulation layer with lesser reliability. In an additionalembodiment of the present invention, the base stations 12, 16 bothtransmit nominal resolution broadcast data using the modulation layerwith greater reliability, and transmit enhanced resolution broadcastdata using the modulation layer with lesser reliability. In an alternateembodiment of the present invention, the base stations 12, 16 bothtransmit basic programming data using the modulation layer with greaterreliability, and transmit supplemental programming data using themodulation layer with lesser reliability. In yet another embodiment ofthe present invention, the base stations 12, 16 both may transmitbroadcast video data. In an alternate embodiment of the presentinvention, the base stations 12, 16 may both transmit broadcast audiodata.

In one embodiment of the present invention, the higher modulation layerdata may include RF communications system control channel data. The basestations 12, 16 may both transmit broadcast data using lower modulationsymbols 48, and the first base station 12 may transmit unicast datadirected to the first mobile terminal 20 using higher modulation symbols50. In an alternate embodiment of the present invention, the second basestation 16 may transmit unicast data directed to the second mobileterminal 28 using one of the modulation symbols 48, 50, and transmitunicast data directed to the third mobile terminal 32 using the other ofthe modulation symbols 48, 50. The modulation layer with greaterreliability is used with the data link with the lower signal margin, andthe modulation layer with lower reliability is used with the data linkwith the greater signal margin. For example, a user close to a basestation may have high reliability for both modulation layers; however, amore distant user may only have sufficient reliability for the lowerorder modulation layer; therefore, be assigning a voice call to thehigher order modulation layer for the close user and a voice call to thelower order modulation layer for the distant user, both users can beaccommodated.

The present invention includes transmitting different information usingdifferent modulation layers. Different embodiments will allocate thedifferent information to the different modulation layers in differentways. Those skilled in the art will understand the concepts of theinvention and will recognize applications of these concepts beyond thespecific examples given. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims. Specifically, the different information may beassociated with any of the different modulation layers in any order.

FIG. 7A shows the alignment of lower modulation layer data 102 withhigher modulation layer data 104 in one embodiment of the presentinvention. The lower modulation layer data 102 includes a first lowerlayer sample 106, a second lower layer sample 108, a third lower layersample 110, and a fourth lower layer sample 112. The higher modulationlayer data 104 includes a first higher layer sample 114, a second higherlayer sample 116, a third higher layer sample 118, and a fourth higherlayer sample 120. The lower layer samples 106, 108, 110, 112 are timealigned with the higher layer samples 114, 116, 118, 120. In mixing asystem with phase and amplitude modulation, such as QAM, with a systemhaving only phase modulation, such as QPSK, the constellation points ofthe QAM system may not directly align with the constellation points ofthe QPSK system; therefore, time-shifting the lower modulation layerdata 102 from the higher modulation layer data 104 may improve signalmargins. In an alternate embodiment of the present invention, the lowermodulation layer data 102 is time-shifted from the higher modulationlayer data 104 as illustrated in FIG. 7B. The higher layer samples 114,116, 118 are time-shifted from the lower layer samples 106, 108, 110,112, which may help average the higher layer samples 114, 116, 118 tomake the lower layer samples 106, 108, 110, 112 line up closer tonominal constellation points of the QPSK system. A lower modulation ratefor the lower modulation layer data 102 may further improve the impactof averaging. Even though the lower modulation layer data 102 istime-shifted from the higher modulation layer data 104, which means thelower modulation symbol 48 is time-shifted from the higher modulationsymbol 50, both modulation symbols 48, 50 fall within one modulationsymbol period and are effectively transmitted simultaneously.

FIG. 8A shows time multiplexed or TDM data included in the highermodulation layer data 104. The higher modulation layer data 104 includesa first sample of first time multiplexed data 122, a first sample ofsecond time multiplexed data 124, a second sample of first timemultiplexed data 126, and a second sample of second time multiplexeddata 128. The samples 122, 126 of the first time multiplexed data areinterspersed with the samples 124, 128 of the second time multiplexeddata. Different channels, sub-channels, or unrelated data streams may beincluded in the higher modulation layer data 104. Other embodiments ofthe present invention may include TDM data in the higher modulationlayer data 104, the lower modulation layer data 102, or both.

FIG. 8B shows two OFDM sub-carriers included in the higher modulationlayer data 104. The higher modulation layer data 104 includes a firstsample of a first OFDM sub-carrier 130, a first sample of a second OFDMsub-carrier 132, a second sample of the first OFDM sub-carrier 134, anda second sample of the second OFDM sub-carrier 136. The samples 130, 134of the first OFDM sub-carrier are interspersed with the samples 132, 136of the second OFDM sub-carrier. Other embodiments of the presentinvention may include OFDM data in the higher modulation layer data 104,the lower modulation layer data 102, or both.

FIG. 9 adds MIMO antennas to the base stations and some of the terminalsillustrated in FIG. 1. The first base station 12 includes a secondantenna port ANT2 coupled to a first MIMO base station antenna 138. Thesecond base station 16 includes a second antenna port ANT2 coupled to asecond MIMO base station antenna 140. The first mobile terminal 20includes a second antenna port ANT2 coupled to a first MIMO mobileterminal antenna 142. The fixed terminal 24 includes a second antennaport ANT2 coupled to a fixed MIMO antenna 144. The third mobile terminal32 includes a second antenna port ANT2 coupled to a second MIMO mobileterminal antenna 146. The second mobile terminal 28 does not have a MIMOantenna. The RF communications system 10 illustrated in FIG. 9 mayrepresent a communications system that has been upgraded to include MIMOcapability. The second mobile terminal 28 does not have MIMO capabilityand may represent a previous generation UE, or may be a low cost,reduced functionality UE sold for use in the MIMO RF communicationssystem 10. By using the present invention, the second mobile terminal 28may be able to transmit and receive lower modulation layer data 102 toand from the base stations 12, 16, and the other terminals 20, 24, 32may be able to transmit and receive both modulation layer data 102, 104to and from the base stations 12, 16.

The present invention includes processing different information streamsusing different modulation layers, such as MIMO. MIMO systems usemultiple antennas for each base station or terminal. The multipleantennas may provide spatial diversity, which allows spatialmultiplexing. Spatial multiplexing may allow different information to betransmitted and received from each of the multiple antennas. Othersystems may use multiple antennas for diversity. Data from singleantenna systems, such as the RF communications system 10 illustrated inFIG. 1, is known as SISO data. Data from multiple antenna systems thathas different information associated with each antenna, such as the RFcommunications system 10 illustrated in FIG. 9, is known as MIMO data.By using SISO data with the lower modulation layer data 102 and MIMOdata with the higher modulation layer data 104, the RF communicationssystem 10 may be backward compatible by supporting previous generationcommunications protocols and present communications protocols.

FIG. 10 shows SISO data included in the lower modulation layer data 102,and two MIMO sub-channels included in the higher modulation layer data104. The lower modulation layer data 102 includes a first SISO datasample 148, a second SISO data sample 150, a third SISO data sample 152,and a fourth SISO data sample 154. The higher modulation layer data 104includes a first sample of a first MIMO sub-channel 156, a first sampleof a second MIMO sub-channel 158, a second sample of the first MIMOsub-channel 160, and a second sample of the second MIMO sub-channel 162.The samples 156, 160 of the first MIMO sub-channel are interspersed withthe samples 158, 162 of the second MIMO sub-channel. Other embodimentsof the present invention may include MIMO data in the higher modulationlayer data 104, the lower modulation layer data 102, or both.

FIG. 11 shows one embodiment of the present invention used with MIMOtransmitter circuitry 164. First transmit circuitry 166 receives bothlower modulation layer data LML and first higher modulation layer dataHML₁. The first transmit circuitry 166 provides a first modulated RFsignal to a first power amplifier 168, which provides an amplified firstmodulated RF signal to the first antenna port ANT1. The first modulatedRF signal is based on both the lower modulation layer data LML and thefirst higher modulation layer data HML₁. Second transmit circuitry 170receives both the lower modulation layer data LML and second highermodulation layer data HML₂. The second transmit circuitry 170 provides asecond modulated RF signal to a second power amplifier 172, whichprovides an amplified second modulated RF signal to the second antennaport ANT2. The second modulated RF signal is based on both the lowermodulation layer data LML and the second higher modulation layer dataHML₂. The lower modulation layer data LML is sent to both antenna portsANT1, ANT2. The first higher modulation layer data HML₁ is sent to onlythe first antenna port ANT1. The second higher modulation layer dataHML₂ is sent to only the second antenna port ANT2. In one embodiment ofthe present invention, the lower modulation layer data LML includesbasic broadcast data, the first higher modulation layer data HML₁includes first supplemental data, and the second higher modulation layerdata HML₂ includes second supplemental data. The second mobile terminal28 may receive the basic broadcast data, and the other terminals 20, 24,32 may receive the basic broadcast data, the first supplemental data,and the second supplemental data. All of the modulation layer data LML,HML₁, HML₂ is transmitted simultaneously. Each of the first and secondhigher modulation layer data HML₁, HML₂ is a MIMO sub-channel. The RFcommunications system 10 may have multiple base stations such that eachbase station has multiple antennas providing MIMO capability. All of thebase stations and antennas may be used to form an SFN using the samelower modulation layer data LML. The first and second higher modulationlayer data HML₁, HML₂ may be transmitted from different base stations,or an antenna on one base station may transmit the first highermodulation layer data HML₁ and an antenna on a different base stationmay transmit the second higher modulation layer data HML₂.

FIG. 12 shows details of the first base station 12 illustrated inFIG. 1. The basic architecture of the first base station 12 may includea receiver front end 174, a radio frequency transmitter section 176, anantenna 178, a duplexer or switch 180, a baseband processor 182, acontrol system 184, and a frequency synthesizer 186. The receiver frontend 174 receives information bearing radio frequency signals from one ormore remote transmitters provided by other base stations, terminals, orother user equipment. A low noise amplifier (LNA) 188 amplifies thesignal. A filter circuit 190 minimizes broadband interference in thereceived signal, while down conversion and digitization circuitry 192down converts the filtered, received signal to an intermediate orbaseband frequency signal, which is then digitized into one or moredigital streams. The receiver front end 174 typically uses one or moremixing frequencies generated by the frequency synthesizer 186. Thebaseband processor 182 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 182 is generallyimplemented in one or more digital signal processors (DSPs).

On the transmit side, the baseband processor 182 receives digitizeddata, which may represent voice, data, or control information, from thecontrol system 184, which it encodes for transmission. The encoded datais output to the transmitter 176, where it is used by a modulator 194 tomodulate a carrier signal that is at a desired transmit frequency. Poweramplifier circuitry 196 amplifies the modulated carrier signal to alevel appropriate for transmission, and delivers the amplified andmodulated carrier signal to the antenna 178 through the duplexer orswitch 180.

The following description provides an overview of a wirelesscommunication environment and the architecture of a base station, orlike access point, and a mobile terminal, which may be used in an OFDMand MIMO environment.

With reference to FIG. 13, a base station controller (BSC) 198 controlswireless communications within multiple cells 200, which are served bycorresponding base stations (BS) 202. In general, each base station 202facilitates communications using OFDM with mobile terminals 204, whichare within the cell 200 associated with the corresponding base station202. The movement of the mobile terminals 204 in relation to the basestations 202 results in significant fluctuation in channel conditions.As illustrated, the base stations 202 and mobile terminals 204 mayinclude multiple antennas to provide spatial diversity forcommunications.

A high level overview of the mobile terminals 204 and base stations 202of the present invention is provided prior to delving into structuraland functional details. With reference to FIG. 14, a base station 202configured according to one embodiment of the present invention isillustrated. The base station 202 generally includes a control system206, a baseband processor 208, transmit circuitry 210, receive circuitry212, multiple antennas 214, and a network interface 216. The receivecircuitry 212 receives radio frequency signals bearing information fromone or more remote transmitters provided by mobile terminals 204.Preferably, a low noise amplifier and a filter (not shown) cooperate toamplify and remove broadband interference from the signal forprocessing. Downconversion and digitization circuitry (not shown) willthen downconvert the filtered, received signal to an intermediate orbaseband frequency signal, which is then digitized into one or moredigital streams.

The baseband processor 208 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 208 is generallyimplemented in one or more DSPs or application-specific integratedcircuits (ASICs). The received information is then sent to an associatednetwork via the network interface 216 or transmitted to another mobileterminal 204 serviced by the base station 202.

On the transmit side, the baseband processor 208 receives digitizeddata, which may represent voice, data, or control information, from thenetwork interface 216 under the control of the control system 206, andencodes the data for transmission. The encoded data is output to thetransmit circuitry 210, where it is modulated by a carrier signal havinga desired transmit frequency or frequencies. A power amplifier (notshown) will amplify the modulated carrier signal to a level appropriatefor transmission, and deliver the modulated carrier signal to theantennas 214 through a matching network (not shown). Modulation andprocessing details are described in greater detail below. In oneembodiment of the present invention, the base station 202 transmitssignals using both antennas 214, but receives signals using a singleantenna 214.

With reference to FIG. 15, a mobile terminal 204 configured according toone embodiment of the present invention is illustrated. Similarly to thebase station 202, the mobile terminal 204 will include a control system218, a baseband processor 220, transmit circuitry 222, receive circuitry224, multiple antennas 226, and user interface circuitry 228. Thereceive circuitry 224 receives radio frequency signals bearinginformation from one or more base stations 202. Preferably, a low noiseamplifier and a filter (not shown) cooperate to amplify and removebroadband interference from the signal for processing. Downconversionand digitization circuitry (not shown) will then downconvert thefiltered, received signal to an intermediate or baseband frequencysignal, which is then digitized into one or more digital streams.

The baseband processor 220 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations, as will be discussed in greater detail below. Thebaseband processor 220 is generally implemented in one or more DSP,ASIC, or both.

For transmission, the baseband processor 220 receives digitized data,which may represent voice, data, or control information, from thecontrol system 218 or the interface circuitry 228, which it encodes fortransmission. The encoded data is output to the transmit circuitry 222,where it is used by a modulator to modulate a carrier signal that is ata desired transmit frequency or frequencies. A power amplifier (notshown) will amplify the modulated carrier signal to a level appropriatefor transmission, and deliver the modulated carrier signal to theantennas 226 through a matching network (not shown). In one embodimentof the present invention, the mobile terminal 204 receives signals usingboth antennas 226, but transmits signals using a single antenna 226.Various modulation and processing techniques available to those skilledin the art are applicable to the present invention.

In OFDM modulation, the transmission band is divided into multiple,orthogonal carrier waves. Each carrier wave is modulated according tothe digital data to be transmitted. Because OFDM divides thetransmission band into multiple carriers, the bandwidth per carrierdecreases and the modulation time per carrier increases. Since themultiple carriers are transmitted in parallel, the transmission rate forthe digital data, or symbols, on any given carrier is lower than when asingle carrier is used.

OFDM modulation may require the performance of an Inverse DiscreteFourier Transform (IDFT) on the information to be transmitted. Fordemodulation, the performance of a Discrete Fourier Transform (DFT) onthe received signal is required to recover the transmitted information.In practice, the IDFT and DFT may be provided by digital signalprocessing carrying out an Inverse Fast Fourier Transform (IFFT) andFast Fourier Transform (FFT), respectively. Accordingly, thecharacterizing feature of OFDM modulation is that orthogonal carrierwaves are generated for multiple bands within a transmission channel.The modulated signals are digital signals having a relatively lowtransmission rate and capable-of staying within their respective bands.The individual carrier waves are not modulated directly by the digitalsignals. Instead, all carrier waves are modulated at once by IFFTprocessing.

In one embodiment, OFDM is used for at least the downlink transmissionfrom the base stations 202 to the mobile terminals 204. Each basestation 202 is equipped with n transmit antennas 214, and each mobileterminal 204 is equipped with m receive antennas 226. Notably, therespective antennas can be used for reception and transmission usingappropriate duplexers or switches and are so labeled only for clarity.

With reference to FIG. 16, a logical OFDM transmission architecture isprovided according to one embodiment. Initially, the base stationcontroller 198 may send channel quality indicator (CQI) informationbased on carrier-to-interference ratios (CIR) to the base station 202.Additionally, the base station controller 198 will send data to betransmitted to various mobile terminals 204 to the base station 202. Thebase station 202 may use the CQIs associated with the mobile terminalsto schedule the data for transmission as well as select appropriatecoding and modulation for transmitting the scheduled data. The CQIs maybe provided by the mobile terminals 204 or determined at the basestation 202 based on information provided by the mobile terminals 204.In either case, the CQI for each mobile terminal 204 is a function ofthe degree to which the channel amplitude (or response) varies acrossthe OFDM frequency band.

Scheduled data 230, which is a stream of bits, is scrambled in a mannerreducing the peak-to-average power ratio associated with the data usingdata scrambling logic 232. A cyclic redundancy check (CRC) for thescrambled data is determined and appended to the scrambled data usingCRC adding logic 234. Next, channel coding is performed using channelencoder logic 236 to effectively add redundancy to the data tofacilitate recovery and error correction at the mobile terminal 204.Again, the channel coding for a particular mobile terminal 204 is basedon the CQI. The channel encoder logic 236 may use known Turbo encodingtechniques in one embodiment. The encoded data is then processed by ratematching logic 238 to compensate for the data expansion associated withencoding.

Bit interleaver logic 240 systematically reorders the bits in theencoded data to minimize the loss of consecutive data bits. Theresultant data bits are systematically mapped into corresponding symbolsdepending on the chosen baseband modulation by mapping logic 242.Preferably, QAM, QPSK, or higher modulation is used. The degree ofmodulation is preferably chosen based on the CQI for the particularmobile terminal. The symbols may be systematically reordered to furtherbolster the immunity of the transmitted signal to periodic data losscaused by frequency selective fading using symbol interleaver logic 244.

At this point, groups of bits have been mapped into symbols representinglocations in an amplitude and phase constellation. When spatialdiversity is desired, blocks of symbols are then processed by space-timeblock code (STC) encoder logic 246, which modifies the symbols in afashion making the transmitted signals more resistant to interferenceand more readily decoded at a mobile terminal 204. The STC encoder logic246 will process the incoming symbols and provide n outputscorresponding to the number of transmit antennas 214 for the basestation 202. The control system 206 and/or baseband processor 208 willprovide a mapping control signal to control STC encoding. At this point,assume the symbols for the n outputs are representative of the data tobe transmitted and capable of being recovered by the mobile terminal204. See A. F. Naguib, N. Seshadri, and A. R. Calderbank, “Applicationsof space-time codes and interference suppression for high capacity andhigh data rate wireless systems,” Thirty-Second Asilomar Conference onSignals, Systems & Computers, Volume 2, pp. 1803-1810, 1998, which isincorporated herein by reference in its entirety.

For the present example, assume the base station 202 has two antennas214 (n=2) and the STC encoder logic 246 provides two output streams ofsymbols. Accordingly, each of the symbol streams output by the STCencoder logic 246 is sent to a corresponding IFFT processor 248,illustrated separately for ease of understanding. Those skilled in theart will recognize that one or more processors may be used to providesuch digital signal processing, alone or in combination with otherprocessing described herein. The IFFT processors 248 will preferablyoperate on the respective symbols to provide an inverse FourierTransform. The output of the IFFT processors 248 provides symbols in thetime domain. The time domain symbols are grouped into frames, which areassociated with a prefix by like insertion logic 250. Each of theresultant signals is up-converted in the digital domain to anintermediate frequency and converted to an analog signal via thecorresponding digital up-conversion (DUC) and digital-to-analog (D/A)conversion circuitry 252. The resultant (analog) signals are thensimultaneously modulated at the desired RF frequency, amplified, andtransmitted via the RF circuitry 254 and antennas 214. Notably, pilotsignals known by the intended mobile terminal 204 are scattered amongthe sub-carriers. The mobile terminal 204, which is discussed in detailbelow, will use the pilot signals for channel estimation.

Reference is now made to FIG. 17 to illustrate reception of thetransmitted signals by a mobile terminal 204. Upon arrival of thetransmitted signals at each of the antennas 226 of the mobile terminal204, the respective signals are demodulated and amplified bycorresponding RF circuitry 256. For the sake of conciseness and clarity,only one of the two receive paths is described and illustrated indetail. Analog-to-digital (A/D) converter and down-conversion circuitry258 digitizes and downconverts the analog signal for digital processing.The resultant digitized signal may be used by automatic gain controlcircuitry (AGC) 260 to control the gain of the amplifiers in the RFcircuitry 256 based on the received signal level.

Initially, the digitized signal is provided to synchronization logic262, which includes coarse synchronization logic 264, finesynchronization logic 266, and frequency offset and clock estimationlogic 268. The coarse synchronization logic 264 buffers several OFDMsymbols and calculates an auto-correlation between the two successiveOFDM symbols. A resultant time index corresponding to the maximum of thecorrelation result determines a fine synchronization search window,which is used by fine synchronization logic 266 to determine a preciseframing starting position based on the headers. The output of the finesynchronization logic 266 facilitates frame acquisition by framealignment logic 270. Proper framing alignment is important so thatsubsequent FFT processing provides an accurate conversion from the timeto the frequency domain. The fine synchronization algorithm is based onthe correlation between the received pilot signals carried by theheaders and a local copy of the known pilot data. Once frame alignmentacquisition occurs, the prefix of the OFDM symbol is removed with prefixremoval logic 272 and resultant samples are sent to frequency offsetcorrection logic 274, which compensates for the system frequency offsetcaused by the unmatched local oscillators in the transmitter and thereceiver. The synchronization logic 262 may include the frequency offsetand clock estimation logic 268, which is based on the headers to helpestimate such effects on the transmitted signal and provide thoseestimations to the correction logic 274 to properly process OFDMsymbols.

At this point, the OFDM symbols in the time domain are ready forconversion to the frequency domain using FFT processing logic 276. Theresults are frequency domain symbols, which are sent to processing logic278. The processing logic 278 extracts the scattered pilot signal usingscattered pilot extraction logic 280, determines a channel estimatebased on the extracted pilot signal using channel estimation logic 282,and provides channel responses for all sub-carriers using channelreconstruction logic 284. In order to determine a channel response foreach of the sub-carriers, the pilot signal is essentially multiple pilotsymbols that are scattered among the data symbols throughout the OFDMsub-carriers in a known pattern in both time and frequency. FIG. 18illustrates an exemplary scattering of pilot symbols among availablesub-carriers over a given time and frequency plot in an OFDMenvironment.

Continuing with FIG. 17, the processing logic compares the receivedpilot symbols with the pilot symbols that are expected in certainsub-carriers at certain times to determine a channel response for thesub-carriers in which pilot symbols were transmitted. The results areinterpolated to estimate a channel response for most, if not all, of theremaining sub-carriers for which pilot symbols were not provided. Theactual and interpolated channel responses are used to estimate anoverall channel response, which includes the channel responses for most,if not all, of the sub-carriers in the OFDM channel. The frequencydomain symbols and channel reconstruction information, which are derivedfrom the channel responses for each receive path, are provided to an STCdecoder 286, which provides STC decoding on both receive paths torecover the transmitted symbols. For the sake of conciseness andclarity, only one of the two receive paths is described and illustratedin detail. The channel reconstruction information provides equalizationinformation to the STC decoder 286 sufficient to remove the effects ofthe transmission channel when processing the respective frequency domainsymbols.

The recovered symbols are placed back in order using symbolde-interleaver logic 288, which corresponds to the symbol interleaverlogic 244 of the transmitter. The de-interleaved symbols are thendemodulated or de-mapped to a corresponding bitstream using de-mappinglogic 290. The bits are then de-interleaved using bit de-interleaverlogic 292, which corresponds to the bit interleaver logic 240 of thetransmitter architecture. The de-interleaved bits are then processed byrate de-matching logic 294 and presented to channel decoder logic 296 torecover the initially scrambled data and the CRC checksum. Accordingly,CRC logic 298 removes the CRC checksum, checks the scrambled data intraditional fashion, and provides it to the de-scrambling logic 300 forde-scrambling using the known base station de-scrambling code to recoverthe originally transmitted data 302.

In parallel to recovering the data 302, a CQI, or at least informationsufficient to create a CQI at the base station 202, is determined andtransmitted to the base station 14. As noted above, the CQI in apreferred embodiment is a function of the CIR, as well as the degree towhich the channel response varies across the various sub-carriers in theOFDM frequency band. For this embodiment, the channel gains for eachsub-carrier in the OFDM frequency band being used to transmitinformation are compared relative to one another to determine the degreeto which the channel gain varies across the OFDM frequency band.Although numerous techniques are available to measure the degree ofvariation, one technique is to calculate the standard deviation of thechannel gain for each sub-carrier throughout the OFDM frequency bandbeing used to transmit data.

Continuing with FIG. 17, a relative variation measure may be determinedby providing the channel response information from the channelestimation logic 282 to a channel variation analysis function 304, whichwill determine the variation and channel response for each of thesub-carriers in the OFDM frequency band, and if standard deviation isused, calculate the standard deviation associated with the frequencyresponse. As noted, channel gain is a preferred measure of the channelresponse for calculating a CQI 306. The channel gain may be quantifiedbased on a relative amplitude of the channel frequency response indecibels (dB), and as such, the amplitude of the channel frequencyresponse may be represented by H_(dB)(k), which is a function of asub-carrier index k, where k=1 . . . k_(MIN), . . . k_(MAX), . . .k_(FFT). Notably, k_(FFT) is the number of sub-carriers in the entireOFDM frequency band, and the sub-carriers k_(MIN) through k_(MAX)represent the sub-carriers within the OFDM frequency band that areactually used to transmit data. Typically, a range of sub-carriers ateither end of the range of sub-carriers are not used, in order tominimize interference with other transmissions. As such, the degree ofvariation of the amplitude of the channel response may be determinedonly for the range of sub-carriers being used to transmit data (k_(MIN)through k_(MAX)). The standard deviation of the channel response acrossthe usable range of sub-carriers is calculated as follows:

$\begin{matrix}{{{std} = \sqrt{\frac{1}{N_{u} - 1}{\sum\limits_{k_{MIN}}^{k_{MAX}}\left( {{H_{dB}(k)} - {\overset{\_}{H}}_{dB}} \right)^{2}}}},} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

where N_(u) is the number of usable sub-carriers, H_(dB)(k) is the logamplitude of the channel frequency response, and H _(db) is the mean ofthe log amplitude of the channel response across the usable range ofsub-carriers or a subset thereof.

In a MIMO system where there are multiple transmit and multiple receiveantennas 214, 226, each link corresponding to transmit/receive antennapairs will have a unique CQI. An aggregate CQI, or set of aggregateCQIs, may be required for the overall MIMO set of links. To determinethe aggregate CQIs, the channel frequency response and CIR for eachtransmit and receive antenna pair is determined.

For multiple receive antennas 226, the multiple channel frequencyresponses are combined to provide for the diversity achieved from themultiple receive antennas 226. This combining is an averaging of thepower of the respective channel frequency responses across the OFDMfrequency band. The channel variation measure is then determined acrossthe combined channel frequency response. The CIR values for therespective multiple receive antennas 226 are combined by summing.

For multiple transmit antennas 214, the modification to the CQI willdepend on the particular space time coding technique employed to reflectthe method by which the transmit diversity is being achieved by the codeand used by the system. Some schemes, such as transmit diversity, willrequire that the respective channel frequency responses from themultiple transmit antennas 214 be combined as described for the multiplereceive antennas 226 by averaging the power of the channel frequencyresponses across the OFDM frequency band. The channel variation measureis made across the combined frequency response. Further, the CIR valuesfor the multiple transmit antennas 214 are also combined. For otherschemes, a separate CQI may be determined for each transmit antenna 214and relayed back to the base station 202. The base station 202 may usethe CQI per transmit antenna 214 to separately adapt the modulation andcoding on the data transmitted on the respective transmit antennas 214.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present invention. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

1. A communication system comprising at least one base station, the atleast one base station comprising transmit circuitry operable to:transmit first data using a first modulation layer of a first carrierradio frequency (RF) signal during a first time period; and initiatetransmission of second data using a second modulation layer of the firstcarrier RF signal during the first time period; wherein the first andsecond modulation layers are hierarchical modulation layers of the firstcarrier RF signal, and the first and second data are processeddifferently.
 2. The system of claim 1, wherein the transmit circuitry isoperable to alternate between transmitting using a single modulationlayer and transmitting using both the first and second modulationlayers.
 3. The system of claim 1, wherein the at least one base stationhas a plurality of antennas forming a single frequency network (SFN). 4.The system of claim 1, wherein the at least one base station has a firstantenna and a second antenna, wherein the first data is transmittedusing the first and second antennas, and the second data is transmittedusing only the first antenna.
 5. The system of claim 4, wherein thefirst data comprises at least one program channel for a basic programservice and the second data comprises at least one program channel for asupplemental program service.
 6. The system of claim 4, wherein thefirst data comprises single-input single-output (SISO) data and thesecond data comprises multiple-input multiple-output (MIMO) data.
 7. Thesystem of claim 4, wherein the at least one base station is operable totransmit third data using only the second antenna.
 8. The system ofclaim 4, further comprising another base station, the other base stationcomprising: third transmit circuitry operable to transmit third datausing a third modulation layer of a second carrier radio frequency (RF)signal during a second time period; and fourth transmit circuitryoperable to initiate transmission of fourth data using a fourthmodulation layer of the second carrier RF signal during the second timeperiod; wherein the third and fourth modulation layers are hierarchicalmodulation layers of the second carrier RF signal, and the third andfourth data are processed differently.
 9. The system of claim 1, whereinat least one of the first data and the second data comprises timemultiplexed data.
 10. The system of claim 1, wherein at least one of thefirst data and the second data is modulated onto a plurality ofsub-carriers using orthogonal frequency division multiplexing (OFDM).11. The system of claim 1, wherein at least one of the first data andthe second data is modulated onto a plurality of sub-carriers usingsingle-carrier frequency division multiplexing (SC-FDM).
 12. The systemof claim 1, wherein the at least one base station has a first antennaand a second antenna, the second data comprises third data and fourthdata, and the transmit circuitry is operable to: transmit the first datausing the first and second antennas; transmit the third data using onlythe first antenna; and transmit the fourth data using only the secondantenna.
 13. The system of claim 1, further comprising at least onerelay station operable to receive the first carrier RF signal.
 14. Thesystem of claim 13, wherein the second data comprises synchronizationinformation.
 15. The system of claim 13, wherein a first of the at leastone relay station is operable to: receive the second data at the secondmodulation layer; and transmit the second data to at least one of agroup consisting of at least one other of the at least one relaystation, user equipment, and the at least one base station.
 16. Thesystem of claim 1, further comprising another base station, the otherbase station comprising transmit circuitry operable to: transmit thefirst data using a third modulation layer of a second carrier radiofrequency (RF) signal during a second time period; and initiatetransmission of third data using a fourth modulation layer of the secondcarrier RF signal during the second time period; wherein the third andfourth modulation layers are hierarchical modulation layers of thesecond carrier RF signal.
 17. The system of claim 1, wherein the firstdata comprises data Unrelated to the second data.
 18. The system ofclaim 1, wherein the first data comprises a different type of mediacontent than the second data.
 19. The system of claim 1, wherein thefirst carrier RF signal comprises a plurality of modulation symbols,such that certain of the plurality of modulation symbols comprises firstorder bits that provide the first data and second order bits thatprovide the second data.
 20. The system of claim 1, wherein the secondmodulation layer is time-shifted from the first modulation layer. 21.The system of claim 21, wherein a modulation rate of the firstmodulation layer is less than a modulation rate of the second modulationlayer.
 22. The system of claim 1, further comprising user equipment (UE)operable to receive the first carrier RF signal.